For many years in commercial pipe clean out operations, a cutting or clearing head 1 (as shown in FIG. 1) has been forced down an underground pipe 2 with a flexible sewer cable 3 that is advanced by a technician 4 from a portable rotating drum or reels 5. The sewer cable 3 is rotated so that the cutting head 1 will clear roots 6, debris and other obstructions. Therefore the sewer cable 3 must be constructed so that it is capable of transmitting substantial torque generated by a powerful electric motor (not illustrated) and transferred through a belt and/or gear drive (not illustrated). The sewer cable 3 must also be sufficiently stiff to enable it to be forced down the pipe 2 as much as approximately one hundred feet or more yet must also be flexible enough to negotiate turns 2a and 2b having a relatively tight radius.
One form of conventional sewer cable 7 (FIG. 2) comprises an elongate flexible steel helical spring. FIG. 3A illustrates another prior art sewer cable 8 comprising an inner core made of a smaller elongate helical steel spring 9 and a jacket made of a larger elongate helical steel spring 10 wound in a direction opposite that of the core 9. FIG. 3B illustrates another prior art sewer cable 11 having a central aircraft cable 12 surrounded by the smaller helical spring 9 which is in turn surrounded by the larger helical spring 10. FIG. 3C illustrates another prior art sewer cable 13 similar to the sewer cable 11 of FIG. 3B, except that the sewer cable 13 of FIG. 3C includes a central aircraft cable 12 surrounded by a plastic or elastomeric jacket 14 made of Nylon, for example.
Conventional sewer cables are typically very heavy. This is a great disadvantage when a plumber or other technician must manually carry upstairs a snake system including fifty to one hundred feet, or more, of sewer cable. Conventional sewer cables are also not well adapted for connection to different heads such as cutting heads, jetting heads and camera heads. Moreover sewer cables currently in commercial use can be dangerous in the event that they kink between the head and the drum or a loop flies free and ensnares the technician. The risk of injury is increased where close laid windings are used in the coil springs in order to increase the torque transmission capabilities of a sewer cable. Conventional sewer cables tend to shorten and lengthen during clean out operations, making it extremely difficult to incorporate electrical conductors that do not end up shorting.